Wind the axle nut back a bit from the adjuster, about 3mm should be enough, and hit the nut with a soft hammer, leather or rubber. Brass will probably damage the castellated nut. When the nut is against the adjuster again, wind it back again & repeat wit the hammer. Do this until the nut is about 2/3 off the axle. Any more & you risk damaging the threads. Time now for a drift. Brass is best, and smaller diameter than the axle. Support the wheel so the axle is always perfectly aligned. Good luck.